Shadowing Variables

[Laloo Bond]

   
package ShadowVariable;
 
 class Foo {
    
static int size=7;
 
static void changeIt(int size){
    size = size + 200;
    System.out.println("size inside changeIt " + size);
}
 
    public static void main(String[] args) {
        System.out.println("Before modify size variable " + size);
        changeIt(size);
        System.out.println("size After changeIt " + size);
    }
}

The output of this program is :
-------------------------------
Before modify size variable 7
size inside changeIt 207
size After changeIt 7


Am little bit confused about the behaviour of this program's output.
As per my knowledge,here SIZE is a static variable and it should be unique.
I believe that is main purpose of static variables and it is accessed globally without creating instance of it.

But here in the changeIt(int size) method, as soon as we create the local(method) variable as the same name of static variable, the global variable is shadowed(hidden) by the local variable.

I thought the output is like :
Before modify size variable7
size inside changeIt207
size After changeIt 207

because size is global variable and unique as it is static.

Could you please explain how it is working and what is the priority and scope of both method(local) variable and static(global) variable.

[edit]Add code tags. CR[/edit]

[ June 20, 2008: Message edited by: Campbell Ritchie ]
[ June 20, 2008: Message edited by: Laloo Bond ]

[Ronald Schild]

Remember that a variable passed as argument is always a copy. In the function, the size is a copy and shadows the static size. You can do anything with it, but the original size variable is not affected.

Try to use the code tags

class Foo {
 
  static int size=7;
 
  static void changeIt(int size){ // the size argument shadows the size above
    size = size + 200; // this is applied to the copy that shadows the original
    System.out.println("size inside changeIt " + size);
 
    // Here, the copy of size ceases to exist and the original size is still 7
  }
 
  public static void main(String[] args) {
    System.out.println("Before modify size variable " + size);
    changeIt(size);
    System.out.println("size After changeIt " + size);
  }
}

[Campbell Ritchie]

Welcome to JavaRanch, Laloo but please don't post the same question twice. I have closed your duplicate thread.
As Ronald Schild has already told you, make sure to use the CODE button (below the "message" window) for quoted code; I have amended your post so you can see how much easier it is to read.

You have actually got two variables called size inside your changeIt method, one which is a (static) field and one which is a parameter. The parameter (as you have been told) shadows the field (a local variable would behave similarly), so the JVM "sees" the parameter only; to it size means the parameter. If you want it to mean the field you would have to write Foo.size (for an instance field write this.size).

[Ronald Schild]

Originally posted by Campbell Ritchie:
Welcome to JavaRanch, Laloo but please don't post the same question twice. I have closed your duplicate thread.
As Ronald Schild has already told you, make sure to use the CODE button (below the "message" window) for quoted code; I have amended your post so you can see how much easier it is to read.

Please make sure you include the package statement in the code tags.

(couldn't resist, sorry it's friday and I'm almost heading home )

[Keith Nagle]

Originally posted by Ronald Schild:


Please make sure you include the package statement in the code tags.

(couldn't resist, sorry it's friday and I'm almost heading home )

jeez, what time zone are you in?
Happy Friday!!

[Campbell Ritchie]

Originally posted by Keith Nagle:
jeez, what time zone are you in?

Obviously one ahead of yours

[Laloo Bond]

Thanks for everyone , who replied and guided me how to post a message with proper readability for the code part in the message.

am in APAC timezone

Now its time for me to think about and enjoy the weekend..

Happy Weekend ...

cheers